Studies on the genes involved in inner ear development should increase our understanding of human inner ear defects resulting in deafness and/or impairment of vestibular function. Although teleosts have a much reduced portion of the inner ear devoted to auditory reception, the vestibular portion of the inner ear is remarkably similar to that of mammals. Furthermore, the fundamental structure of the sensory epithelium is conserved in fish and mammals. The zebrafish embryo offers a number of advantages in the identification of genes that may be involved in inner ear defects, and in the experimental testing of the function of genes known to be expressed during the development of the inner ear. This proposal continues work that has been carried out in our laboratory on zebrafish inner ear development. We propose four Specific Aims. The first Aim directly continues our work on fate mapping of the specialized structures of the inner ear. In addition to completion of the fate map of the 24 hpf otic vesicle, we will carry out fate mapping of statoacoustic and anterior lateral line ganglia precursors. We will also trace cell movements and determine relative proliferation rates for various otic vesicle territories. These studies with wildtype embrv are essential to understand the cellular defects of mutants with defects in inner ear development. The se ond Aim continues our work on dog-eared, a gene we have demonstrated by positional candidate gene cloning to encode the Eyes Absent 1 (Eyal) protein. This finding demonstrates that the zebrafish is an excellent model for the study of human deafness disorders since mutations of the human EYA1 result in branchio-oto-renal syndrome. It is thus likely that other zebrafish inner ear mutants will be ot great relevance to the study of human deafness and vestibular disorders. In the third Aim of the proposal, we propose to molecularly identify quadro, a gene required for proper formation of the otic placode. quadro mutant embryos develop defects in otic placodal precursors between 12 and 13 hpf, resulting in a failure to properly express early markers of the placode and the dispersal and fragmentation of placodal tissue. We will apply the methods successfully utilized for dog-eared to the mapping and characterization of the quadro gene. The fourth aim of the proposal is a continuation of our mutant screen for defects in otic vesicle formation and patterning.